If the Skull comes back, he has better be far more evil like he is the comics. I think they kinda ruined the Skull in the first movie by distancing him from the Nazis too quickly. In the comics, Red Skull only gave up on Nazism decades later, feeling it had become outdated, but the Skull was still a Nazi in WWII and was Hitler's second in command, so he was fully involved with the crimes the Nazis committed. In the movie, that wasn't the case, so it made the Skull seem far less evil then he was in the comics.

wait... I thought he left them, because they weren't evil enough for his tastes?